Mastering Astronomy Chapter 5 HW

Suppose you watch a leaf bobbing up and down as ripples pass it by in a pond. You notice that it does two full up and down bobs each second. Which statement is true of the ripples on the pond?

They have a frequency of 2 hertz (two cycles per second)

An atom which has 4 protons and 6 neutrons will be electrically neutral if it contains __________.

4 electrons

Suppose you have a 100-watt light bulb that you leave turned on for one minute. How much energy does it use?

6,000 joules To find this answer, remember that 1 watt = 1 joule/s, so a 100-watt light bulb uses 100 joules of energy per second. In 1 minute, it uses 60 ( 100 = 6,000 joules of energy. Return to Assignment

Which of the following statements is true of green grass?

It absorbs red light and reflects green light.

Suppose you had molecular oxygen (O2) chilled enough so that it was in liquid form. Which of the following best describes the phase changes that would occur as you heated the liquid oxygen to high temperature?

It would vaporize (evaporate) into a gas, then the molecules would dissociate into individual oxygen atoms, then the atoms would become increasingly ionized as you continued to raise the temperature.

Betelgeuse is the bright red star representing the left shoulder of the constellation Orion. All the following statements about Betelgeuse are true. Which one can you infer from its red color?

Its surface is cooler than the surface of the Sun.

Which of the following conditions lead you to see an absorption line spectrum from a cloud of gas in interstellar space?

The cloud is cool and lies between you and a hot star.

The diagram represents energy levels in a hydrogen atom. The labeled transitions (A through E) represent an electron moving between energy levels. If an electron at level 1 in a hydrogen atom absorbs 10.2 eV of energy, it moves to level 2. What typically happens next?

The electron returns to level 1 by emitting an ultraviolet photon with 10.2 eV of energy.

Which of the following statements about thermal radiation is always true?

A hot object emits more radiation per unit surface area than a cool object.

Which of the following transitions within an atom is not possible?

An electron begins in an excited state and then gains enough energy to jump to the ground state.

Choose the correct definition of electrical charge.

Electrical charge is a measure of how strongly something will interact with electromagnetic fields.

Under what circumstances can energy level transitions occur?

Electrons can make a transition from one level to another by taking in or emitting a specific amount of energy. If too much or too little energy is offered, the electron cannot make the transition.

Which of the following statements about electrons is not true?

Electrons orbit the nucleus rather like planets orbiting the Sun.

Why doesn't a microwave oven make a plastic dish get hot? Why do some clay dishes get hot in the microwave? Why do dishes that aren't themselves heated by the microwave oven sometimes still get hot when you heat food on them? (Note: It's not a good idea to put empty dishes in a microwave.)

Microwave ovens are tuned to emit frequencies absorbed by water molecules, not by a plastic dish. Some clay dishes contain some water inside them. Conduction from heated food heats the dish.

Which of the following procedures would allow you to make a spectrum of the Sun similar to the one shown, though with less detail? In the illustration of the solar spectrum, the upper left portion of the spectrum shows the __________ visible light.

Pass a narrow beam of sunlight through a prism. (The prism bends different wavelengths of light by different amounts, causing the white light from the Sun to spread out into a rainbow of colors. Absorption features appear as dark lines against the brighter background of the spectrum.) lowest frequency (Red light is the longest wavelength visible light, and longer wavelength means lower frequency (because wavelength×frequency=speed of lightwavelength×frequency=speed of light)

What is the difference between energy and power?

Power is the rate at which energy is used, so its units are a unit of energy divided by a unit of time.

Suppose that Star X and Star Y both have redshifts, but Star X has a larger redshift than Star Y. What can you conclude?

Star X is moving away from us faster than Star Y. The redshifts mean that both stars are moving away from us, and a larger redshift means a faster speed.

Suppose that two stars are identical in every way; for example, same distance, same mass, same temperature, same chemical composition, and same speed relative to Earth, except that one star rotates faster than the other. Spectroscopically, how could you tell the stars apart?

The faster rotating star has wider spectral lines than the slower rotating star.

Which of the following best describes why we say that light is an electromagnetic wave?

The passage of a light wave can cause electrically charged particles to move up and down.

If we observe one edge of a planet to be redshifted and the opposite edge to be blue-shifted, what can we conclude about the planet?

The planet is rotating. We see a blueshift from the side rotating toward us and a redshift from the side rotating away. Return to Assignment

Suppose you are listening to a radio station that broadcasts at a frequency of 97 MHz (megahertz). Which of the following statements is true?

The radio waves from the radio station are causing electrons in your radio's antenna to move up and down 97 million times each second. Submit

Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?

The star is moving toward us (blue shift)

All of the following statements about the Sun's corona are true. Which one explains why it is a source of X-rays?

The temperature of the corona's gas is some 1 to 2 million Kelvin (high energy light)

Studying a spectrum from a star can tell us a lot. All of the following statements are true except one. Which statement is not true?

The total amount of light in the spectrum tells us the star's radius.

Which of the following best describes the fundamental difference between two different chemical elements (such as oxygen and carbon)?

They have different numbers of protons in their nucleus.

If a distant galaxy has a substantial redshift (as viewed from our galaxy), then anyone living in that galaxy would see a substantial redshift in a spectrum of the Milky Way Galaxy.

This statement makes sense. The redshift means that we see the galaxy moving away from us, so observers in that galaxy must also see us moving away from them—which means they see us redshifted as well.

Choose the correct explanation of an electron and a proton or two electrons attracting or repelling one another.

We define a proton as having +1 unit of charge and an electron as having -1 unit when talking about atoms and particles. Two particles with charges of different sign will attract each other, so protons and electrons will attract. Particles with charges of the same sign will repel each other, so two electrons will repel each other.

What do we mean when we say that energy levels are quantized in atoms?

We mean that the electrons can have only discrete values of electrical potential energy in atoms.

Which of the following statements about x-rays and radio waves is not true?

X-rays travel through space faster than radio waves.

No object produces a perfect thermal radiation spectrum, but many objects produce close approximations. Which of the following would not produce a close approximation to a thermal radiation spectrum?

a hot, thin (low-density, nearly transparent) gas

Consider an atom of carbon in which the nucleus contains six protons and seven neutrons. What is its atomic number and atomic mass number?

atomic number = 6; atomic mass number = 13

Absorption examples

blue light hits a red sweatshirt; visible light does not pass through a black wall

Ionization is the process by which

electrons escape from atoms.

Emission examples

light comes from your computer screen; light comes from a lightbulb

Red light has a _____ wavelength and a _____ frequency than does blue light.

longer, lower

Suppose that you had "X-ray vision" that allowed you to see X rays. What would you notice when you looked at a friend standing near you that you could not notice with your visible light vision alone?

nothing

Thermal radiation is defined as __________.

radiation with a spectrum whose shape depends only on the temperature of the emitting object

If you have a telescope that is observing light with wavelengths of a few meters, you are observing __________.

radio waves

Reflection or scattering examples

red light hits a red sweatshirt; white light hits a white piece of paper

X ray photons have a _____ wavelength, _____ frequency, and _____ energy than do ultraviolet photons.

shorter, higher, higher

Suppose you want to know the chemical composition of a distant star. Which piece of information is most useful to you?

the wavelengths of spectral lines in the star's spectrum

Transmission examples

visible light and clear glass; cell phone signals passing through walls